1. Field of the Invention
The present invention relates to footwear and, more particularly, to a safety footwear which is adapted to dissipate electrostatic charges while at the same time protecting the wearer against electric shocks.
2. Description of the Prior Art
It is known to wear static dissipative shoes, for instance, to prevent electrostatic charges build up upon the body and clothing from being discharged to an electrostatic sensitive device being handled. Such static dissipative shoes are widely used in the electronic and computer industries to prevent damaging of electronic components, such as integrated circuits, by electrical discharges.
U.S. Pat. Nos. 4,366,630 and 4,785,371 respectively issued on Jan. 4, 1983 and Nov. 15, 1988 to Bloom and Edwards both disclose an electrostatically dissipating shoe having a composite sole including a conductive insole and a conductive outsole of rubber or plastic materials doped with an electrically conductive substance and connected together in electrically conductive relationship. U.S. Pat. No. 4,785,371 also teaches that the overall resistance across the composite sole should be in a range of about 106 to 108 ohms to not expose the wearer to the undue risk of injury from electrical contact, as would conventional conductive footwear exhibiting an overall resistance from zero to about 104 ohms.
U.S. Pat. No. 2,712,099 issued on Feb. 23, 1952 to Legge discloses a footwear having metallic grounding members for conducting electrostatic charges from the body of the wearer to the ground. Resistors are provided as safety device to prevent the passage of a current of high amperage from the grounding members to the wearer""s body.
Although the electrostatically dissipating shoes described in the above mentioned patents are effective, it has been found that there is a need for a new electrostatically dissipating footwear having a relatively low electrical resistance between the wearer""s foot and ground, while still providing protection against electrical shocks.
It is therefore an aim of the present invention to provide a composite sole for a safety footwear which is, adapted to dissipate electrostatic charges while at the same time protecting the wearer against potential electric shocks.
It is also an aim of the present invention to provide a safety footwear which is comfortable to wear.
It is a further aim of the present invention to provide an electrostatically dissipating sole having a relatively low electric resistance.
It is still a further aim of the present invention to provide a new method of manufacturing an electrostatically dissipating sole for a safety footwear.
Therefore, in accordance with the present invention, there is provided a composite sole for use in a safety footwear, comprising an insole and an outsole, said insole and said outsole being at least partly made of electrically-conducting material, an insulator provided between said insole and said outsole, and an electronic device integrated between said insole and said outsole for dynamically controlling current flow therebetween, said electronic device including a resistor for setting the electrical resistance of an electrically conductive path define by said insole, said outsole and said electronic device; and a microfuse for protecting the wearer against electrical shocks, wherein said microfuse includes a fusible wire having a cross-sectional area smaller or equal to about 1xc3x9710xe2x88x9211 m2, said fusible wire being adapted to melt at a predetermined amperage to break said electrically conductive path, thereby protecting the wearer against electrical shocks.
In accordance with a further general aspect of the present invention, there is provided a composite sole for use in an electrostatic dissipative footwear, comprising an insole and an outsole spaced by a mid sole, said insole and said outsole being at least partly made of electrically-conducting material, whereas said mid sole is made of a substantially non-conductive material, and an electronic device extending through said mid sole for connecting said insole and said outsole in electrically conductive relationship, said electronic device including a resistor for controlling current flow between said insole and said outsole, and a fuse for protecting the wearer against electrical shocks, wherein said fuse is embedded in said mid sole which acts therefor as an insulator.
In accordance with a further general aspect of the present invention there is provided a method of manufacturing an electrostatically dissipating sole for a safety footwear, comprising the steps of: providing a conductive insole and a conductive outsole, providing an electronic device in a free space between said insole and said outsole for controlling current flow therebetween, connecting said insole and said outsole in electrically conductive relationship with said electronic device, and structurally joining said insole to said outsole by injecting a substantially non-conductive material in said free space to form a mid sole between said insole and said outsole with said electronic device at least partly embedded in said mid sole.